The document U.S. Pat. No. 6,679,286 discloses an assembly comprising:                a tank containing a liquid, such as oil,        and a level sensor of such liquid, comprising:                    a float movable along guide means and which can float on the liquid of the tank or on a volume of the liquid in communication with the liquid in the tank, according to the principle of communicating vessels, so that the float can move along with the liquid level in the tank,            at least one permanent magnet movable with the float,            an electronic card provided with magnetic switches sensitive to said magnet.                        
One problem raised by this system is that, in the event of off-centering over the length of the guide means, the compensation of coaxiality tolerances relative to the upper centering may be provided by the liquid level sensor which supports the stress resulting from the misalignment by deforming. This deformation may weaken the sensor and result in the breaking thereof.
Reinforcing the sensitive areas of the sensor may then be required. Such reinforcement, however, increases the mass of the sensor, which affects the tank design (mechanical behaviour) and therefore the engine consumption. And this problem is even more important when the tank is rigidly mounted on the engine (no shock damper). The vibrations experienced by the sensor are then higher, thus causing more constraints in the sensor.
Another problem relates to the risks of the float getting stuck along its guide means.
As a matter of fact, some clearance is left between the float and the tube so that the float can slide along the guide means (a tube in U.S. Pat. No. 6,679,286). Now, if the float gets stuck by becoming askew along the tube, the oil level information provided by the sensor is then invalid because the float no longer follows the change in height of the oil remaining in the tank.